zram: avoid lockdep splat by revalidate_disk

Sasha reported lockdep warning [1] introduced by [2].

It could be fixed by doing disk revalidation out of the init_lock.  It's
okay because disk capacity change is protected by init_lock so that
revalidate_disk always sees up-to-date value so there is no race.

[1] https://lkml.org/lkml/2014/7/3/735
[2] zram: revalidate disk after capacity change

Fixes 2e32baea46ce ("zram: revalidate disk after capacity change").

Signed-off-by: Minchan Kim <minchan@kernel.org>
Reported-by: Sasha Levin <sasha.levin@oracle.com>
Cc: "Alexander E. Patrakov" <patrakov@gmail.com>
Cc: Nitin Gupta <ngupta@vflare.org>
Cc: Jerome Marchand <jmarchan@redhat.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
CC: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 089e72c..36e54be 100644 (file)
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -622,11 +622,18 @@ static void zram_reset_device(struct zram *zram, bool reset_capacity)
        memset(&zram->stats, 0, sizeof(zram->stats));
 
        zram->disksize = 0;
-       if (reset_capacity) {
+       if (reset_capacity)
                set_capacity(zram->disk, 0);
-               revalidate_disk(zram->disk);
-       }
+
        up_write(&zram->init_lock);
+
+       /*
+        * Revalidate disk out of the init_lock to avoid lockdep splat.
+        * It's okay because disk's capacity is protected by init_lock
+        * so that revalidate_disk always sees up-to-date capacity.
+        */
+       if (reset_capacity)
+               revalidate_disk(zram->disk);
 }
 
 static ssize_t disksize_store(struct device *dev,
@@ -666,8 +673,15 @@ static ssize_t disksize_store(struct device *dev,
        zram->comp = comp;
        zram->disksize = disksize;
        set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);
-       revalidate_disk(zram->disk);
        up_write(&zram->init_lock);
+
+       /*
+        * Revalidate disk out of the init_lock to avoid lockdep splat.
+        * It's okay because disk's capacity is protected by init_lock
+        * so that revalidate_disk always sees up-to-date capacity.
+        */
+       revalidate_disk(zram->disk);
+
        return len;
 
 out_destroy_comp: